FIELD: manufacture of building materials, particularly, granular heat-insulating material, especially light filling agent for concrete. SUBSTANCE: granular heat-insulating material is prepared by method comprising preparation and granulation of raw mix and subsequent thermal treatment. Raw mix is prepared from microsilica which is crystalline silicon with particle size of (0.01-01,1)×10-6m which comprises 83-93 wt.% of SiO2 and 6-16 wt.% of carbon impurities, sodium hydroxide solution and water preheated to 85-95 C at 1:5 liquid and solid phases of 0.813-1.0, and heat treatment is carried out at temperatures from 350 to 400 C for 20-30 min. EFFECT: shorter duration of heat treatment of raw granules, simplified production process for producing granular heat-insulating material and reduced bulk density thereof. 2 tbl
